风雪环境下高海拔山区公路桥上车辆侧向安全性研究

Sichuan-Tibetan mountain area is high in altitude and complex in terrain. Due to the combined influence of complex terrain and plateau climate, the high wind period coincides with the snowfall period, which poses a serious threat to the lateral safeties of the vehicles on the bridges. To clear the safety of the vehicles moving on highway bridge in Sichuan-Tibetan mountain area under wind and snow, four basic contents are required to be studied, including the rules of deck shape and aerodynamic forces after snow deposition, the flow and aerodynamic characteristics on vehicle-bridge system in wind and snow, the distribution of roughness and lateral friction on the high altitude bridge under snow and ice, the lateral safety conditions of the vehicles on the high altitude bridge and the corresponding reliability. This project focuses on the above contents. Firstly, combined with wind tunnel tests and numerical simulations, the characteristics of accumulated snow and their influence on the aerodynamic forces of main girders during and after snowfall will be revealed. The flow law, aerodynamic characteristics, and influence factors with wind and snow about the road vehicle-bridge system during and after the snowfall will be cleared. Later on, field tests will be conducted on the high altitude bridges, and the spatial distribution and the statistical characteristics of the roughness and the lateral friction on the decks under snow and ice will be explored. Eventually, the safety conditions and corresponding probability reliability about the vehicles moving on the high altitude highway Bridge will be determined, based on the wind-vehicle -bridge dynamic coupling system.

川藏山区海拔高、地形复杂，受地形与高原气候的共同影响，大风期与降雪期高度重合，公路桥上车辆的侧向安全性面临着较为严重的威胁。为明确风雪作用下川藏山区公路桥梁的行车安全性，四个基础性内容亟待研究，包括：桥梁积雪形态与积雪后气动力变化规律、风雪共同作用下车—桥组合系统绕流及气动力特征、高海拔桥梁积雪结冰下桥面粗糙度及侧向摩擦力分布特点、风雪环境下桥上车辆侧向安全条件及可靠度。本项目针对上述内容开展研究。首先，结合风洞试验与数值模拟两种手段，揭示降雪过程中、降雪停止后主梁积雪的特点及对气动力的影响规律，明确公路车辆—桥梁组合系统的风雪绕流规律、气动力特点及影响因素。其次，开展高海拔桥梁桥面现场测试，探明积雪结冰状态下桥面粗糙度及侧向摩擦力的空间分布规律及统计特征。再次，以公路风—车—桥动力耦合系统为基础，确定风雪环境下高海拔公路桥上车辆侧向安全性的条件及概率可靠性。

本研究针对风雪环境下高海拔山区公路桥上车辆侧向安全性研究开展工作，主要工作包括：1）基于小时空尺度局部均衡假定，提出了估算近地雪相质量浓度分布的吹雪预测模型，建立了风雪双向耦合三维数学模型，开展风洞试验验证了数值模型的合理性；确定了典型箱形主梁积雪的侵蚀与沉积状态,明确了积雪前后主梁气动力的变化规律。2）提出了指数脉冲风速识别桥梁气动导纳的数值方法；推导了雪颗粒对理想平板断面的撞击力，确定了风雪两相流作用下理想平板的气动力；探索了积雪效应对车-桥组合系统气动力系数的影响。3）提出了自然降雪风洞模拟试验装置，建立反映真实特性的轮胎-地面接触模型；研究了时变温度下桥面结冰状态和摩擦系数。4）提出了确定性激励作用下结构参数随机动力分析的维数自适应数值积分方法，提出了线性结构非平稳随机振动时域分析方法；提出了时变车桥系统非平稳随机振动分析方法；建立桥上车辆侧向安全评估方法，获得雪冰条件下的行车安全可靠性。得出以下主要结论：吹雪预测模型对不同风雪环境具有较好的稳定性，风雪双向耦合模型较好的反映雪颗粒间的黏附状态。桥面积雪风致重分布特征主要体现在外形突变局部位置的积雪堆积与其它位置的侵蚀，风速越大堆积与侵蚀越显著。积雪重分布改变桥面外形，光顺了公路箱梁桥面线形，导致主梁阻力系数降低、升力系数增大明显。铁路桥面因桥面轨道等附属设施更为复杂，积雪形态对主梁气动力的影响较为复杂。积雪加强了车底旋涡结构，导致车-桥组合系统中主梁力矩系数增加，车辆阻力系数减小、升力系数显著增加。桥面结冰时，轮台-桥面摩擦系数具有明显时变特性，不同车重、车速下摩擦系数具有一定差异。所提出的参数随机、激励随机、车桥耦合随机振动方法准确可靠，具有良好的计算效率，计算获得了基于可靠度的桥面行车安全参考条件。研究成果具有一定的学术意义和实用价值。